Back analysis of a natural jointed rock slope based on the photogrammetry method

Abstract

In 2013, a potentially unstable jointed rock slope above a road in the Gold Coast area, Australia, partially failed after a rainfall event. In this study, the rock failure was back analysed to evaluate the presence of key blocks through block analysis based on photogrammetry surveys. Friction angles of the joint sets at the point of failure were also investigated by means of a parametric study using a 3D distinct element method (DEM). The photogrammetry method was employed to obtain measurements of the orientation of the joint sets of the slope and the shape and size of rock blocks at the inaccessible slope. The joint roughness coefficient (JRC) obtained from the 3D photogrammetry model was utilised to estimate friction angles and the strength of the joint set. Safety factors of the rock mass were computed by both analytical and numerical approaches. Parametric analyses, using a DEM model, assessed the critical friction angle of the joint sets and also demonstrated the failure mechanism of the blocks. The result of this study indicates that the obtained safety factors are in agreement with the block analysis and the results from the numerical analysis performed by the distinct element code "3DEC".